The invention relates to a method of controlling packet transmission in conjunction with a packet radio service in a radio system comprising a base station and a number of subscriber terminals transmitting data to the base station in packet form using the same transmission channel, in said method the base station transmitting packets to the terminals and said packets comprising data indicating to which terminal each packet is intended, actual data, and control data controlling the transmission of the terminals on the transmission channel.
In conjunction with radio systems, packet radio services refer to a service employing packet switched technique known from fixed networks. Commercial radio systems used are commonly circuit-switched. Circuit switching is a method in which a connection is created between the users by allocating a predetermined amount of transmission capacity to the connection. During the entire connection, the transmission capacity is allocated exclusively to the connection. Packet switching is a method in which a connection is created between the users by transmitting data in packets comprising address and control data. Several connections can simultaneously employ the same transmission connection. The usage of packet switched radio systems particularly in transmitting data has been an object of research in recent years, since the packet switching method is well suited for data transmission required in software, in which the data to be transmitted is generated in bursts. In such a case the data transmission connection does not have to be reserved for the entire time, only for the packet transmission. Considerable savings in cost and capacity can be achieved by this, both when a network is being constructed and when it is being used.
Packet radio networks are presently particularly interesting when the GSM system is being developed further; reference is then made to the GPRS (General Packet Radio Service). The ETSI GSM specification proposal (ETSI GSM 03.64, Version 1.2.0, Mar. 3, 1997) describes the air interface in the GPRS between the network portion and the subscriber terminal.
In the GSM system, one physical channel is one time slot in a TDMA frame. The TDMA frame has eight time slots. According to the ETSI GSM 03.64 specification proposal, one or several physical channels, a PDCH (Packet Data Channel) which in practice is a traffic channel, are defined for setting up a packet radio connection and for packet transmission. Logical channels are located in the PDCH. The logical channels are divided into PCCCH channels (Packet Common Control Channel) and packet traffic channels. The packet traffic channels comprise PDTCH channels (Packet Data Traffic Channel) and PACCH channels (Packet Associated Control Channel). The PCCH channels comprise PRACH (Packet Random Access Channel) channels, PPCH (Packet Paging Channel) channels, PAGCH (Packet Access Grant Channel) channels and PBCCH (Packet Broadcast Control Channel) channels.
The system reserves resources from a radio path for different transmission directions asymmetrically, in other words independently of each other. In the uplink direction, in other words from a terminal to a base station, the radio path can be simultaneously employed by more than one terminal, and in such a case the terminals compete for the use of the channel. The system controls the use of the radio path in such a manner that the base station transmits data packets to the terminals, and these packets comprise data indicating to which terminal each packet is intended. The packets further comprise control data controlling the transmission of the terminals on the transmission channel.
Since the transmissions in different transmission directions are independent of each other, a situation may easily arise in which a terminal has something to be transmitted, but the base station has no data to be transmitted to the terminals. In a prior art solution the terminals cannot, however, transmit since they are not receiving data from the base station indicating the user of the radio path. In such a case, the terminals are compelled to wait for the base station to transmit data to a terminal. Radio path resources are thus used rather inefficiently at the moment.
An object of the present invention is therefore to provide a method by means of which the radio path resources can be utilized more efficiently than before.
This is achieved by the method of the type described in the introduction, the method being characterized in that when there is no actual data, a base station transmits packets comprising control data of the transmission but no actual data to the terminals.
The method of the invention has several advantages. By means of the invention the traffic in different transmission directions can be controlled independently of whether a base station has data to be transmitted to the terminals. Uplink capacity can thus be substantially increased.